Electric motor

ABSTRACT

An electric motor comprising a rotor having plural magnetic poles in the circumferential direction; and a stator whose teeth are disposed opposite to the periphery of the rotor, with an air gap interposed between the rotor and the stator, wherein the coil conductors are wound on the stator so that two stator magnetic poles may be formed by two coil units of a phase wound around stator teeth within the range of 360 electrical degrees subtended by the magnetic poles of the rotor; each of the two coil units forming the stator magnetic poles spans an electrical angle less than 180 electrical degrees; the two coil turns forming the two stator magnetic poles are laid out so that they may not overlap each other; and the coil conductors are so wound that the adjacent stator magnetic poles exhibit opposite magnetic polarities.

BACKGROUND OF THE INVENTION

This invention relates to an electric rotating machine and especially toan electric motor.

Coils of distributed winding and concentrated winding are well known asthey are used as stator coils for electric rotating machines. Forexample, JP-A-6-165422 discloses the twin three-phase coil systemcomprising the first three-phase coil groups wound around the teeth ofthe stator core in the short pitch lap winding and connected with oneanother in the three-phase connection and the second three-phase coilgroups wound around the teeth of the stator core in the short pitch lapwinding and connected with one another in the same three-phaseconnection, the first three-phase coil groups being staggered by 60electrical degrees from the second three-phase coil groups.

SUMMARY OF THE INVENTION

With the recent trend of energy conservation, it has come to be requiredto increase the efficiency in the performance of electric motors. Sincethe disclosed technique employs the concentrated winding structure inprinciple, the stator windings for a single phase link the magnetic fluxgenerated by the rotor only within the range of 120 electrical degrees,having difficulty in obtaining higher efficiency as compared with thesystem using the distributed winding structure which links magnetic fluxover 360 electrical degrees.

On the other hand, in the case of the distributed winding configuration,which includes full and short pitch windings, normally wound coils aresubstantially wound over 180 electrical degrees and reversely woundcoils are wound over the remaining 180 electrical degrees, all the coilsfor the three-phase system being wound on the stator core. With thiscoil structure, the self-linking magnetic flux increases and thereforethe resultant coil inductance becomes relatively large. Accordingly, ifthe coils of distributed winding are used on a generator, currentgeneration is suppressed in the high-speed operating region. If they areused on an electric motor, the response in the control of coil currentbecomes poor.

According to this invention, it is possible to improve the electriccharacteristics of an electric motor.

According to one aspect of this invention, there is provided a statorwithin which a rotor is disposed with an air gap interpose between them,and in which coil conductor is wound such that two stator magnetic polesformed by two coil units of a phase are arranged within the range of 360electrical degrees subtended by the magnetic poles of the rotor. It ispreferable to cause each coil unit forming a stator magnetic pole tospan an electrical angle less than 180 electrical degrees in thecircumferential direction. It is also preferable to arrange the two coilunits in such a manner that their coil turns do not overlap each other.It is further preferable to wind the coil conductor on the stator suchthat the two stator magnetic poles exhibit opposite magnetic polarities.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a first embodiment of an electric motor, withits air gap portion developed linearly along the circumferentialdirection of the rotor;

FIG. 2 schematically shows a second embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIGS. 3A˜3C show an example of how coils are wound on an electric motoraccording to this invention;

FIGS. 4A˜4C show another example of how coils are wound on an electricmotor according to this invention;

FIGS. 5A˜5C show still another example of how coils are wound on anelectric motor according to this invention;

FIGS. 6A˜6C show a further example of how coils are wound on an electricmotor according to this invention;

FIGS. 7A˜7C show a still further example of how coils are wound on anelectric motor according to this invention;

FIGS. 8A˜8C show a yet further example of how coils are wound on anelectric motor according to this invention;

FIGS. 9A˜9C show an additional example of how coils are wound on anelectric motor according to this invention;

FIG. 10 schematically shows a third embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIG. 11 schematically shows a fourth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIG. 12 schematically shows a variation of the electric motor shown inFIG. 11;

FIG. 13 schematically shows another variation of the electric motorshown in FIG. 11;

FIG. 14 schematically shows a fifth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIGS. 15A and 15B show the U-phase windings on the electric motor shownin FIG. 14;

FIG. 16 is the phaser diagram associated with the windings shown inFIGS. 15A and 15B;

FIG. 17 schematically shows a sixth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIGS. 18A and 18B show the U-phase windings on the electric motor shownin FIG. 17;

FIG. 19 is the phaser diagram associated with the windings shown inFIGS. 18A and 18B;

FIG. 20 schematically shows a seventh embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIGS. 21A and 21B show the U-phase windings on the electric motor shownin FIG. 20;

FIG. 22 is the phaser diagram associated with the windings shown inFIGS. 21A and 21B;

FIG. 23 schematically shows an eighth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor;

FIGS. 24A and 24B are the phaser diagrams associated respectively withthe windings of three-phase systems A and B of the electric motors shownin FIG. 23;

FIG. 25 shows in cross section an air-cooled alternator for use on avehicle, as an embodiment of this invention;

FIGS. 26A and 26B show two examples of three-phase rectifier circuitsfor the three-phase windings on the alternator shown in FIG. 25;

FIG. 27 pictorially represents in developed cross section the electricmotor shown in FIG. 2;

FIGS. 28A and 28B schematically show the two different aspects of aninth embodiment of an electric motor, illustrating how coils are woundaround the stator teeth;

FIGS. 29A and 29B schematically show in two different aspects a tenthembodiment of an electric motor, illustrating how coils are wound aroundthe stator teeth;

FIGS. 30A and 30B schematically show in two different aspects aneleventh embodiment of an electric motor, illustrating how coils arewound around the stator teeth; and

FIGS. 31A and 31B schematically show in two different aspects a twelfthembodiment of an electric motor, illustrating how coils are wound aroundthe stator teeth.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following embodiments of this invention relate to electric rotatingmachines such as motors, generators and motor-generators having thefunctions of both a motor and a generator, which are widely used inpower, industry, home and automobile applications.

Electric rotating machines such as generators and motors include variouskinds of generators and motors such as, for example, induction motors,permanent magnet synchronous motors and direct current commutatingmotors. When such an electric rotating machine is used as a generator,the stator and the rotor are made up of windings and iron cores; DCcurrent is made to flow through the windings on the rotor or the rotoris made of permanent magnet, so as to magnetize the rotor; rotatingmagnetic flux is passed throughout the stator by rotating the magnetizedrotor; and magneto-motive force is induced in the windings wound on thestator.

The way of winding coil conductors around the stator teeth serving asstator magnetic poles includes distributed winding and concentratedwinding.

The distributed winding includes full pitch winding and short pitchwinding. In both of full and short pitch distributed windings, coilconductor is normally wound around teeth to form one coil unitsubstantially spanning 180 electrical degrees and then reversely woundaround other teeth to form another coil unit spanning the remaining 180electrical degrees. The coil sides of the coil units of all the phasesare inserted in slots arranged within 180 electrical degrees. In case ofsuch a distributed winding, the magnetic flux generated by the currentflowing through any specific coil unit of the coil group for a phaselinks the turns of the coil units of the coil groups of other phases.Since the flux generated by a coil unit of a phase links the neighboringcoil units of the same phase, the resultant coil inductance becomesrelatively large. Accordingly, if the coils of distributed winding areused on a generator, current generation is suppressed in the high-speedoperating region. If they are used on an electric motor, the response inthe control of coil current becomes poor.

In case of the concentrated winding, on the other hand, the coil groupof one phase is completely separated from the coil group of anotherphase, that is, the coil units of the coil group for a phase are woundaround the teeth that are different from the teeth around which the coilunits of the coil group for another phase are wound. The coil units ofthe coil group for a phase receive about all available flux generatedfrom the stator divided by the number of phases, within the range of 360electrical degrees. For example, in case of three phases, the fluxreceived by the coil group for each phase is ⅓ of all the availableflux. In order to increase the flux linkage, the number of turns of eachcoil unit must be increased. The increase in the number of turns leadsto the increase in the resultant coil inductance, and hence, even incase of the concentrated winding, current generation is suppressed inthe high-speed operating region of a generator while the response in thecontrol of coil current becomes poor in a motor, just as in case of thedistributed winding.

In addition, the concentrated winding has a problem that acoustic noiseduring rotation is relatively large due to the higher harmoniccomponents of electromagnetic force resulting from the armature reactioncaused by the current flowing through the stator coils. Since one of themain causes of the noise is the sixth higher harmonic component ofelectromagnetic force, two three-phase winding systems are employed andthe phase difference φ between the two systems is made equal to 30degrees so as to cancel the sixth higher harmonic component. Since thephase difference φ in the above mentioned conventional technique is 60degrees, it is difficult for the prior art to suppress the sixth higherharmonic component that is one of the main causes of acoustic noise.

Further, since the related art mentioned above employs the concentratedwinding in principle, the coil group for a phase, wound on the stator,can only utilize that part of the magnetic flux which is generated bythe portion of the rotor within 120 electrical degrees, in case of agenerator. Although the distributed winding can utilize the flux over360 electrical degrees, the three-phase concentrated windings utilizeonly a partial amount of the flux.

According to the embodiments of this invention described below, copperloss can be reduced by eliminating the congregation of coil end portionsat both the ends of the stator in its axial direction, so that theoperating efficiency of an electric rotating machine can be increased.

According to the embodiments of this invention described below, theeffect of reducing acoustic noise can be expected since the higherharmonic components of electromagnetic force can be made relativelysmall as compared with the case where the concentrated winding isemployed.

According to the embodiments of this invention described below, in orderto obtain the same induced voltage, that is, under the condition of thesame mutual inductance with respect to the rotor, the self inductance ofcoil groups can be made smaller as compared with the case where thedistributed or concentrated winding is employed. This is because, in theembodiments described below, the coil group for a phase utilizes onlypart of the flux generated by the rotor over 360 electrical degrees, asis different from the distributed winding that distributes coil turnsall over the stator core. Namely, only a part of the flux which aparticular coil group generates links that coil group itself. Since thearea over which a particular coil group faces the magnetic poles of therotor with the concentrated winding is half that which is observed withthe corresponding coil group of the stator windings according to thisinvention, the number of turns in each coil unit must be increased toincrease the induced voltage. Since coil inductance increases with thesquare of the number of coil turns, coil inductance according to theconventional technique is necessarily increased. According to theembodiments of this invention, since self inductances of coils can bemade small, the characteristic of controlling coil currents can beimproved in an electric motor while the characteristic of generatingcurrent can be improved in a generator.

As described in the following embodiments, if this invention is appliedto an alternator for use on an automobile, whose rotational speed rangesfrom a lower limit of 2000 rpm up to a higher limit of 15000 rpm,excellent electrical characteristics can be obtained. The alternator foruse on an automobile generates electric power on the basis of therotational energy of an internal combustion engine to drive theautomobile. Since the range of rotational speeds covered by such analternator is very wide, the impedance resulting from the inductance ofthe stator coils becomes very high in the high speed operation range sothat current generation is suppressed. This suppression of generatedcurrent causes the lowering of operating efficiency. According to theembodiments of this invention described below, the stator coilinductance can be prevented from becoming large, and therefore thecharacteristic of generating current in the high speed operating rangecan be improved.

In the foregoing description, explanation has been made of theimprovement of electric characteristics, but in what follows below asthe embodiments of this invention, problems other than those mentionedabove will be solved and advantages other than those described abovewill be obtained. According to the following embodiments, the number ofturns of each coil unit is small so that if the way of winding isapplied to an alternator used on an automobile, productivity can beimproved. For the reduction in size of an alternator for an automobileis strongly desired since it is installed on the vehicle. According tothe following embodiments, the number of turns of each coil unit can bemade small so that even if the size of the stator is reduced owing tothe requirement for size reduction, productivity remains still high.Moreover, since the number of turns of each coil unit on the stator canbe made small as compared with the conventional structure of statorcoils, the way of structuring stator coils according to this inventioncan be easily matched to the needs for size reduction.

According to the following embodiments, since the number of connectionpoints at which one coil unit or one coil group is connected withanother coil unit or another coil group is small, productivity isexcellent and high reliability can be maintained. Since alternators forautomobiles are usually operated in such severe environments where theyare exposed to the vibrations of the vehicle body due to the ruggednessof road surfaces or the repeated explosive internal combustion of theengine, or where they are exposed to temperatures ranging from belowzero to above boiling point, it is preferable to make the number ofpoints of connection as by welding as small as possible. Moreover, sincethe number of turns of each coil unit is small, the surface area ofexposed coil conductors is large so that heat accumulation occurring asa result of some coil turns being buried among other coil turns can beeasily prevented and therefore heat resistivity is excellent. From thesemany aspects contemplated above, the embodiments of this inventiondescribed in the following will be very suitable for application to analternator for use on an automobile.

This invention will be described below by way of embodiments inreference to the attached drawings.

FIG. 1 schematically shows a first embodiment of an electric motor, withits air gap portion developed linearly along the circumferentialdirection of the rotor. The electric motor comprises a rotor 1 and astator 2 in principle. The rotor 1 has plural rotor magnetic poles 11,and the stator 2 has plural teeth 21 serving as stator magnetic poles.Coil units of U-phase coil group 31, V-phase coil group 32 and W-phasecoil group 33 are wound around teeth 21 of the stator core. It should benoted here that the V-phase coil unit, i.e. an individual coil unit ofthe V-phase coil group, is the coil unit through which flows analternating current having its phase lagging by 120 degrees (or leadingby 240 degrees) from the phase of the current flowing through theU-phase coil unit, i.e. an individual coil unit of the U-phase coilgroup, and that the W-phase coil unit, i.e. an individual coil unit ofthe W-phase coil group, is the coil unit through which flows analternating current having its phase lagging by 240 degrees (or leadingby 120 degrees) from the phase of the current flowing through theU-phase coil unit. In FIG. 1, the direction of revolution of the rotor 1is indicated by an arrow.

It should also be understood that solid line indicates the coil unit ofnormal winding (in which the coil conductor is wound around teethclockwise as viewed radially from the rotor toward the stator), whereasbroken line denotes the coil unit of reverse winding (in which the coilconductor is wound around teeth counterclockwise as viewed radially fromthe rotor toward the stator). As shown in FIG. 1, the coil units ofnormal winding are placed in the slots of the stator 2 remotely from therotor 1, but they may be placed closer to the rotor 1 in the slots. Eachphase coil group consists of a pair of concentrated-wound coil unitsdistanced by 180 electrical degrees from each other within the range of360 electrical degrees. The U-phase coil units are connected in serieswith one another, the V-phase coil units are connected in series withone another, and the W-phase coil units are connected in series with oneanother. In other words, the stator 2 is disposed opposite to the rotor1, with a uniform air gap formed between them; the coil conductors arewound such that two coil units of a phase create two magnetic poles 91and 92 within the region of 360 electrical degrees; each of the two coilunits of a phase forming the stator poles 91 and 92 spans an electricalangle smaller than 180 electrical degrees in the circumferentialdirection of the rotor 1; the coil turns of the two coil units of aphase, forming the two magnetic poles 91 and 92, are placed in thestator slots in such a manner that they do not overlap each other; andthe coil turns of the two coil units of a phase are so wound that thetwo magnetic poles 91 and 92 have opposite polarities. In thisembodiment, the coil units wound around the two stator magnetic poles 91and 92 are disposed at a distance of 180 electrical degrees from eachother. And the stator magnetic poles for the U-, V- and W-phases aredisposed at a distance of 60 electrical degrees from one another. Thedirection of winding coil conductor in each V-phase coil unit isopposite to the direction of winding coil conductor in each U-phase coilunit. Accordingly, the temporal phase of the V-phase coil unit lags thetemporal phase of the U-phase coil unit by 120 degrees since +60degrees−180 degrees=−120 degrees. On the other hand, since the directionof winding coil conductor in each W-phase coil unit is the same as thedirection of winding coil conductor in each U-phase coil unit, thetemporal phase of the W-phase coil unit leads the temporal phase of theU-phase coil unit by 2×60 degrees (=120 degrees). Also, in thisembodiment, each individual coil turn spans 120 electrical degrees, andtwo coil turns of a phase span 240 electrical degrees, that is, twothirds of the entire teeth within the total 360 electrical degrees. Thisway of winding coil conductors will be hereafter termed “dispersedwinding”.

As a result of employing the dispersed winding, the stator windingaccording to this embodiment is featured by the individual coil turnthat has its circuit area linking the magnetic flux issuing from therotor, which circuit area is twice as large as that of the individualcoil turn of the concentrated winding wherein a singleconcentrated-wound coil is provided within the range of 360 electricaldegrees. Thus, the coil utility efficiency of the dispersed winding istwice as large as that of the concentrated winding. For obtaining thesame amount of flux linkage, the number of turns of coil conductorwound, according to this embodiment, around, for example, a singlestator magnetic pole may be half the corresponding number of turns inthe concentrated winding. Each of the U-, V- and W-phase coil groups isdispersed over the range of electrical angles that is double the rangeof electrical angles for each of the U-, V- and W-phase coil groups inthe concentrated winding. Further, different from the distributedwinding wherein coil conductors are wound around all the teeth, coilconductors are wound around, according to this embodiment, two thirds ofthe entire teeth provided within 360 electric degrees. Accordingly, thecoil inductance can be reduced as compared with that developed in theconcentrated winding or the distributed winding.

Moreover, according to this embodiment, the degree of dispersion ofcoils is double that for the concentrated winding, and the U-, V- andW-phase coils are wound with an overlap percentage of about 50%.Accordingly, the armature reaction is distributed relatively uniformlyalong the periphery of the rotor in contrast to that observed with theconcentrated winding, so that the higher harmonic components ofelectromagnetic force can be reduced. For this reason, electric motorsemploying the structure of winding according to this embodiment canoperate with less sonic noise than electric motors employing theconcentrated winding.

In the embodiment shown in FIG. 1, stator teeth are provided at aninterval of 60 electrical degrees and each coil unit spans 120electrical degrees. Alternatively, however, the same advantages can beobtained if stator teeth are provided at an interval of 30 electricaldegrees and if each coil unit spans 90, 120 or 150 electrical degrees.Also, in other embodiments of this invention shown in FIGS. 2 through 9and described below, in each of which a single three-phase system isexemplified, stator teeth are provided at an interval of 60 electricaldegrees and each coil unit spans 120 electrical degrees. It, however,will be needless to say that the same advantages can be obtained ifstator teeth are provided at an interval of 30 electrical degrees and ifeach coil unit spans 90, 120 or 150 electrical degrees.

FIG. 2 schematically shows a second embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor. Except the items described below, this secondembodiment is similar to the first embodiment described above. The wayof winding the stator coils according to this embodiment is differentfrom that according to the first embodiment. Every stator coil turn iswound around teeth 21 in such a manner that one coil side of a coil turnis disposed near the bottom of a slot while the other coil side of thesame coil turn is disposed closer to the top of another slot. Namely, asviewed in the direction along the rotor shaft, the apparent parts of thecoil turns appear slanting as shown in FIG. 2. Thus, the positions ofall the coil elements in the radial direction are evenly distributed. Inother words, the coil inductances of the respective phase coils areaveraged by winding the coils in such a manner that one coil side of acoil turn is disposed near the bottom of a slot, i.e. remote from therotor, while the other coil side of the same coil turn is disposedcloser to the top of another slot, i.e. near the rotor. In the firstembodiment described above, the respective phase coil units are evenlydistributed around teeth 21 in the radial direction by being connectedin series with one another, but, according to this embodiment, therespective phase coil units are evenly distributed before making suchseries connections. FIG. 27 pictorially represents the electric motorshown in FIG. 2. The coil layout within one third of the 360 electricaldegree period repeats so that the phase coil units are distributedevenly over the entire circumferential distance.

The winding structure in which the respective phase coil groups areevenly distributed in the stator slots in the radial direction, is verypreferable in configuring a uniform three-phase AC system.

FIGS. 3A˜3C show an example of how coils are wound on the electricmotors according to this invention. FIGS. 3A˜3C respectively show howthe U-, V- and W-phase coil groups are wound around teeth, as viewed inthe radial direction from the rotor toward the stator enclosing therotor. As shown in these figures, for ease of understanding the way ofwinding coil conductors, the actual thickness of the coil conductor isignored and the one coil turn conductor is spaced from another coil turnconductor. The horizontal direction in the figures corresponds to thecircumferential direction of the stator. In this embodiment, six slots(six teeth) are provided at a regular distance within 360 electricaldegrees, and therefore one slot (tooth) is shifted from another slot(tooth) by 60 electrical degrees.

In this embodiment shown in FIGS. 3A˜3C, each of the coil units of eachphase coil group has its coil conductor wound twice, and spans 120electrical degrees (i.e. two teeth 21) to form a stator magnetic pole 91for one of the three phases. After being wound twice around the teethforming the magnetic pole 91, the coil conductor then leaves the slotwhere it was last inserted. After leaving the last inserted slot, thecoil conductor is inserted in a slot that is distanced by 180 electricaldegrees (i.e. three teeth 21) from the last inserted slot, and startsbeing wound twice around two teeth to form a stator magnetic pole 92.The resulting coil unit also spans 120 electrical degrees and thedirection of winding the coil conductor is reverse to the direction ofwinding the coil conductor in the coil unit forming the magnetic pole91. It should be noted here that “wound twice” means that two coilelements exist in each of the two slots in which each coil unit isinserted. Thus, these two coil units are in series connection with eachother. With this winding configuration, the overall length of coilconductor can be minimized so that the copper loss can be greatlyreduced.

According to this winding configuration, when all the three-phase coilgroups are set in the entire slots formed between the teeth 21, thenumbers of coil elements placed in the respective slots are the samethroughout the stator. Therefore, the coil conductor distribution can bemade uniform without local conductor concentration so that coils can beeasily wound and the cooling of coils can be made uniform in ventilationcooling. It will be needless to say that even if the numbers of coilelements placed in different slots are not the same as one another, thecoil structure of dispersed winding as employed in this embodiment canbe employed.

In this embodiment, the total of four coil elements are inserted in aslot. In the case where the total number of coil elements set in a slotis even, the coil configuration of this embodiment can be applied.

FIGS. 4A˜4C show another example of how coils are wound on the electricmotors according to this invention. Except the items described below,this example is the same as that described above.

In this example, each of the coil units of each phase coil group has itscoil conductor wound two and a half times, and spans 120 electricaldegrees (i.e. two teeth 21) in the circumferential direction to form astator magnetic pole 91 for one of the three phases. After being wound2.5 times around the teeth forming the magnetic pole 91, the coilconductor then leaves the slot where it was last inserted. After leavingthe last inserted slot, the coil conductor is inserted in a slot that isdistanced by 180 electrical degrees (i.e. three teeth 21) from the lastinserted slot, and starts being wound two and a half times around twoteeth to form a stator magnetic pole 92. The resulting coil unit alsospans 120 electrical degrees and the direction of winding the coilconductor is reverse to the direction of winding the coil conductor inthe coil unit forming the magnetic pole 91. It should be noted here that“wound two and a half times” means that two coil elements lie in one ofthe two slots in which a coil unit is inserted while three coil elementslie in the other of the same two slots. With this coil configuration,the coil end portions of all the coil units can be evenly disposed onboth sides in the axial direction of the stator so that the localcongregation of coil end portions can be prevented. In this example, thecoil units each having the coil conductor wound two and a half timesaround teeth are described, but this example can equally be applied tothe case where the number of conductor turns in each coil unit is equalto an integer plus half unity. Also, in this example, the total of fivecoil elements are inserted in each slot. Thus, this example can also beapplied to the case where the number of coil elements inserted in eachslot is odd.

FIGS. 5A˜5C show still another example of how coils are wound on theelectric motors according to this invention. Except the items describedbelow, this example is the same as in the embodiment described above. Inthese figures, arrows put on the coil conductors of two coil groups ofeach phase indicate the directions of currents flowing through therespective phase coil groups at a certain instant of time.

In this example, the normally wound coil group and the reversely woundcoil group are separated from each other. Coil conductor is wound suchthat a normally wound coil unit spans 120 electrical degrees (or twoteeth 21) in the circumferential direction to form a normally woundstator magnetic pole 91. The coil conductor of the normally wound coilunit leaves the last inserted slot; the coil conductor, after leavingthe last inserted slot, enters a slot distanced by 240 electricaldegrees (or four teeth 21) from the last inserted slot; and a coil unithaving two conductor turns is formed by winding the coil conductor twicein the same direction as around the normally wound stator magnetic pole91, to form another stator magnetic pole. In like manner, coil conductoris wound such that a reversely wound coil unit spans 120 electricaldegrees (or two teeth 21) to form a reversely wound stator magnetic pole92 within the region of 240 electrical degrees between the abovedescribed two normally wound coil units, so that the phase of thecurrent through the coil unit wound around the reversely wound statormagnetic pole 92 is shifted by 180 degrees from the phase of the currentthrough the coil unit around the normally wound stator magnetic pole 91.The coil conductor leaves the last inserted slot; the coil conductor,after leaving the last inserted slot, enters a slot distanced by 240electrical degrees (or four teeth 21) from the last inserted slot; and acoil unit having two conductor turns is formed by winding the conductortwice in the same direction as around the stator magnetic pole 92.

It is preferable to connect the normally wound coil groups ofthree-phases in series with one another and to connect the reverselywound coil groups of three-phases in series with one another. By doingso, the end portions of all the coil units can be evenly disposed onboth sides in the axial direction of the stator so that the localcongregation of coil end portions can be prevented. In addition, thework of coil winging is facilitated so that this configuration isexcellent in mass production.

In this example, the total of four coil elements are inserted in eachslot. Thus, this example can also be applied to the case where thenumber of coil elements inserted in each slot is even.

FIGS. 6A˜6C show a further example of how coils are wound on theelectric motors according to this invention. Except the items describedbelow, this example is the same as the example described above. In thesefigures, arrows put on the coil conductors of two coil groups of eachphase indicate the directions of currents flowing through the respectivephase coil groups at a certain instant of time.

In this example, third coil groups, i.e. U-phase coil group 313, V-phasecoil group 323 and W-phase coil group 333, are added to the coilstructure as shown in FIGS. 5A˜5C. The added coil group is in the wavewinding, and each coil unit of the wave winding spans 180 electricaldegrees so that the coil conductor passes through one of the slots inwhich the normally wound coil unit in FIG. 5 is set and one of the slotsin which the reversely wound coil unit in FIG. 5 is set. This way ofwinding coil conductor may be said to be the hybrid of dispersed windingand distributed winding. This hybrid winding has a feature that higherharmonic components can be suppressed to an appreciable extent, thischaracteristic being an advantage obtained with the distributed winding.

In this example, the total of five coil elements are inserted in eachslot. Thus, this example can also be applied to the case where thenumber of coil elements inserted in each slot is odd.

FIGS. 7A˜7C show a further example of how coils are wound on theelectric motors according to this invention. Except the items describedbelow, this example is the same as in the embodiment described above. Inthese figures, arrows put on the coil conductors of four coil groups ofeach phase indicate the directions of currents flowing through therespective phase coil groups at a certain instant of time.

FIGS. 7A˜7C show an example wherein the normally wound coil groups 311and the reversely wound coil groups 312, the normally wound coil groups321 and the reversely wound coil groups 322, and the normally wound coilgroups 331 and the reversely wound coil groups 332, are separated fromeach other, respectively. Two normally wound coil units, both in thewave winding and inserted in the same pair of slots, span 120 electricaldegrees (or two teeth 21) to form a normally wound stator magnetic pole91. The coil conductors of the two normally wound coil units leave thelast inserted slot; the coil conductors, after leaving the last insertedslot, enter a slot distanced by 240 electrical degrees (or four teeth21) from the last inserted slot; and two coil units in the wave windingare formed by winding the coil conductors in the same direction asaround the normally wound stator magnetic pole 91, to form anotherstator magnetic pole. In like manner, two reversely wound coil units,both in the wave winding and inserted in the same pair of slots, span120 electrical degrees (or two teeth 21) to form a reversely woundstator magnetic pole 92 within the region of 240 electrical degreesbetween the above mentioned two slots, so that the phases of thecurrents through the coil units wound around the reversely wound statormagnetic pole 92 are shifted by 180 degrees from the phases of thecurrents through the coil units around the normally wound statormagnetic pole 91. The coil conductors of the two reversely wound coilunits leave the last inserted slot; the coil conductors, after leavingthe last inserted slot, enter a slot distanced by 240 electrical degrees(or four teeth 21) from the last inserted slot; and two coil units inthe wave winding are formed by winding the conductors in the samedirection as around the stator magnetic pole 92. The two coil groupsinserted in the same pairs of slots may be connected in series orparallel with each other, but the coil group consisting of normallywound coil units and the coil group consisting of reversely wound coilunits should preferably be connected in series with each other. By doingso, the end portions of all the coil units can be evenly disposed onboth sides in the axial direction of the stator so that the localcongregation of coil end portions can be prevented. In addition, sincethe wave winding process, not multiple encircling of teeth by windingconductors, is employed, the work of conductor winging is facilitated sothat this configuration is excellent in mass production.

In this example, the total of four coil elements are inserted in eachslot. Thus, this example can also be applied to the case where thenumber of coil elements inserted in each slot is even.

FIGS. 8A˜8C show a yet further example of how coils are wound on theelectric motors according to this invention. Except the items describedbelow, this example is the same as the example described above. In thesefigures, arrows put on the coil conductors of five coil groups of eachphase indicate the directions of currents flowing through the respectivephase coil groups at a certain instant of time.

In this example, third coil groups, i.e. U-phase coil group 313, V-phasecoil group 323 and W-phase coil group 333, are added to the coilstructure as shown in FIGS. 7A˜7C. The added coil groups are in the wavewinding, and each coil unit of the wave winding spans 180 electricaldegrees so that the coil conductor passes through one of the two slotsin which the normally wound coil units in FIG. 7 are set and one of thetwo slots in which the reversely wound coil units in FIG. 7 are set.This way of winding coil conductor may be said to be the hybrid ofdispersed winding and distributed winding. This hybrid winding can enjoya characteristic that higher harmonic components can be suppressed to anappreciable extent, this characteristic being an advantage obtained withthe distributed winding.

In this example, the total of five coil elements are inserted in eachslot. Thus, this example can also be applied to the case where thenumber of coil elements inserted in each slot is odd.

FIGS. 9A˜9C show an additional example of how coils are wound on theelectric motors according to this invention. Except the items describedbelow, this example is the same as the example described above. In thesefigures, arrows put on the coil conductors of four coil groups of eachphase indicate the directions of currents flowing through the respectivephase coil groups at a certain instant of time.

This example is a variation of the example shown in FIGS. 7A˜7C. In thisexample, coil conductors are wound such that the reversely wound coilgroups 312, 322 and 332 as shown in FIGS. 7A˜7C appear to be flippedupside down as seen in FIGS. 9A˜9C, and also the directions of thecurrents through the reversely wound coil groups 312, 322 and 332 arereversed in contrast to the embodiment shown in FIGS. 7A˜7C, so thatvirtual closed circuits whose currents encircle a series of teeth pairs,can be formed with the conductors of the normally wound coil groups 311,321 and 331 and the conductors of the reversely wound coil groups 312,322 and 332.

In this example, the total of four coil elements are inserted in eachslot. Thus, this example can also be applied to the case where thenumber of coil elements inserted in each slot is even.

FIG. 10 schematically shows a third embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor. Except the items described below, thisembodiment is the same as the embodiments described above. The windingstructure employed in this embodiment is the combination of the abovedescribed dispersed winding and the twin three-phase windings. Namely,two systems of three-phase coil groups, each system being similar to thethree-phase coil groups shown in FIG. 1, are so disposed that one coilgroup of one system is shifted in phase from the corresponding coilgroup of the other system. As shown in FIG. 10, twelve (12) teeth areprovided within the range of 360 electrical degrees, that is, twoadjacent teeth are separated from each other by 30 electrical degrees.Coil units of dispersed winding for one three-phase system (three-phasesystem A) are disposed in those portions of teeth 21 which are remotefrom the rotor in the radial direction while coil units of dispersedwinding for the other three-phase system (three-phase system B) aredisposed in those portions of teeth 21 which are less remote from therotor in the radial direction. The coil units of the three-phase systemB are staggered by 30 electrical degrees from the corresponding coilunits of the three-phase system A. The coil conductors of thethree-phase system A and the coil conductors of the three-phase system Bare connected in parallel with each other. In each of the three-phasesystems A and B, each coil unit spans four teeth.

FIG. 11 schematically shows a fourth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor. Except the items described below, thisembodiment is the same as the embodiments described above.

It is preferable to construct the windings of the three-phase system Aand the windings of the three-phase system B equivalently in the senseof electric circuit element. By doing so, the higher harmonic componentsof electromagnetic force can be effectively suppressed. When thiswinding structure is employed in a generator, the output current becomesuniform so that the ripples in the resultant output current can bereduced. To obtain this effect, each coil unit spanning teeth in thecircumferential direction is slanted as viewed in the direction alongthe rotor shaft, as shown in FIG. 11. Thus, the windings of each of thethree-phase systems A and B form stator magnetic poles for therespective phases U, V and W. Two coil units of a phase, separated by 30electrical degrees from each other, have their one coil side disposed inthat portion of a slot which is remote from the rotor and their othercoil side disposed in that portion of another slot which is less remotefrom the rotor, so that the coil ends of the two coil units may notcross each other. With this winding structure, the two three-phasesystems A and B will have equal electric circuit characteristics.

In the embodiment shown in FIG. 11, each coil unit spans four teeth,i.e. 120 electrical degrees, but each coil unit may span three teeth,i.e. 90 electrical degrees, as shown in FIG. 12. Further, each coil unitmay span five teeth, i.e. 150 electrical degrees, as shown in FIG. 13.

If the twin three-phase systems of dispersed winding are employed andthe two three-phase systems are staggered by 30 electrical degrees or sofrom each other, then the sixth harmonic component of electromagneticforce can be effectively suppressed so that the electric rotatingmachine using this winding structure can reduce acoustic noise duringoperation to a great extent.

FIG. 14 schematically shows a fifth embodiment of an electric motor,with its air gap portion developed linearly along the circumferentialdirection of the rotor. Except the items described below, thisembodiment is the same as the embodiments described above.

In the embodiment shown in FIG. 11, six teeth were provided for eachmagnetic pole of the rotor to be fit for the twin three-phase windingstructure. However, this embodiment employs the structure in which threeteeth are provided per magnetic pole of the rotor, to realize the twinthree-phase winding structure. In this embodiment, the basic dispersedwinding structure is partially changed. As shown in FIG. 14, eachnormally wound coil unit in the U-phase coil group of the three-phasesystem A spans three teeth while each reversely wound coil unit in theU-phase coil group of the three-phase system A spans two teeth. On theother hand, each normally wound coil unit in the U-phase coil group ofthe three-phase system B spans two teeth while each reversely wound coilunit in the U-phase coil group of the three-phase system B spans threeteeth. One coil side of each normally wound coil unit and one coil sideof each reversely wound coil unit share the same slot, and the positionsof such shared slots are the same for both the three-phase system A andthe three-phase system B. FIGS. 15A and 15B show how the coil conductoris wound around the stator teeth with respect to the U-phase coil groupsfor both the three-phase system A and the three-phase system B. Anormally wound coil group 314 and a reversely wound coil group 315 ofthe three-phase system A, and a normally wound coil group 317 and areversely wound coil group 316 of the three-phase system B, are all inthe wave winding as shown in FIGS. 15A and 15B, respectively. The numberof the conductor turns of each normally wound coil unit is the same asthat of each reversely wound coil unit. FIG. 16 is the phaser diagramassociated with the U-phase windings of the three-phase systems A and Bshown in FIGS. 15A and 15B, the phaser diagram denoting the magneticfluxes which the U-phase coil groups for both the three-phase system Aand the three-phase system B cut, with their phase relationship takeninto consideration. In FIG. 16, the relative magnitudes of the phasersrepresenting the respective fluxes are given by numerals 6 and 2 wheneach of the normally wound coil unit and the reversely wound coil unithas two coil turns. Vector calculation indicates that 27.8 degrees isthe difference in electrical angle between the phasers representing themagnetic fluxes which the U-phase coil groups for the three-phasesystems A and B cut, respectively. Although the difference angle is abit shifted from 30 degrees, the rate of reduction, in this case, in thesixth harmonic component of electromagnetic vibrating force is given bythe expression:

(1+cos (6×27.8 deg))/2=0.013 or 1.3%

This value means that a sufficient effect of noise reduction has beenobtained, that is, acoustic noise during operation can be suppressed.According to this embodiment, the number of teeth spun by the normallywound coil unit is different from the number of teeth spun by thereversely wound coil unit, in the U-, V- and W-phase coil groups foreach of the three-phase systems A and B. This embodiment has anadvantage that coil winding work is facilitated since the number ofteeth spun by each coil unit need not be doubled.

If the phase difference angle in the twin three-phase system is 20degrees, it holds that

(1+cos (6×20 deg))/2=0.25

If the phase difference angle in the twin three-phase system is 40degrees, it holds that

(1+cos (6×40 deg))/2=0.25

Thus, both cases give the same result, that is, the reduction rate of25% for the sixth harmonic component of electromagnetic vibrating force.Accordingly, if the difference angle is set within a range of 20˜40degrees, the reduction rate for the sixth harmonic component ofelectromagnetic vibrating force can be rendered equal or less than 25%.

Anther embodiment based on the same idea as described above will now beexplained in reference to FIGS. 17˜19. This embodiment is similar to theembodiment shown in FIG. 15, except for the addition of an auxiliarycoil groups. As shown in FIGS. 18A and 18B, all the coil units are inthe wave winding. In this case, too, since the same reduction rate canbe obtained for the sixth harmonic component of electromagneticvibrating force, the same effect as in the above described embodimentcan be obtained.

Still another embodiment based on the same idea as described above willbe briefly explained in reference to FIGS. 20˜22. This embodiment issimilar to that shown in FIGS. 17, except in that the three-phase systemB is modified. As shown in FIGS. 21A and 21B, all the coil units are inthe wave winding. In this case, the reduction rate for the sixthharmonic component of electromagnetic vibrating force can be given by

(1+cos (6×32.2 deg))/2=0.013

Thus, since the same reduction rate as in the previous embodiment can beobtained for the sixth harmonic component of electromagnetic vibratingforce, the same effect as in the above described embodiment can beobtained.

Yet another embodiment based on the same idea as described above will bebriefly explained in reference to FIG. 23. According to this embodiment,the phase difference in electrical angle between the three-phase systemsA and B can be made roughly equal to 30 degrees by slightly shifting thepositions of the coil groups for the three-phase system A from thepositions of the coil groups for the three-phase system B. Theassociated phaser diagrams shown in FIGS. 24A and 24B indicate that thephase difference in electrical angle between the three-phase systems Aand B is 43.9−16.1=27.8 (deg). The corresponding reduction rate for thesixth harmonic component of electromagnetic vibrating force is given by

(1+cos (6×27.8 deg))/2=0.013

Therefore, the same effect as in the above described embodiment can beobtained. The coil structure shown in FIG. 23 is only schematicallydepicted, and it will be needless to say that even if all the coil unitsare radially shifted in position as desired for ease of coil windingwork, the sixth harmonic component of electromagnetic vibrating forcecan be effectively reduced.

Any of the above described embodiments can be widely used in electricmotors and generators for use in power, industry, domestic and vehicleapplications. To be concrete, high-rated examples include windmillgenerators, vehicle driving motors and industrial rotating machines;mid-rated ones include rotating machines used for industrial applicationand auxiliary equipment on vehicles; and low-rated ones include electricrotating machines for use in OA devices.

An embodiment in which this invention is concretized as a generator willnow be described. By employing such a twin three-phase system asdescribed above, output currents containing less ripples can beobtained.

FIG. 25 shows in cross section an air-cooled alternator for use on avehicle, as an embodiment of this invention. A rotor 1 has nail-shapedmagnetic poles 113 provided around a shaft, and a field winding 112 iswound around the central part of the nail-shaped magnetic poles 113. Apulley 101 is attached to one end of the shaft, and slip rings 109 forenergizing the field winding are mounted on the other end of the shaft.A cooling fan system consisting of a front fan 107F and a rear fan 107R,which are rotated in synchronism with the rotor 1, is attached to thenail-shaped magnetic poles 113. The nail-shaped magnetic poles 113 areprovided with permanent magnets 116 for auxiliary excitation to add tothe flux generated by the field winding. A stator 2 comprises statormagnetic poles 91, 92 and a stator winding. The stator 2 is disposedopposite to the rotor 1, with a thin air gap defined between them. Thestator 2 is supported by a front bracket 114 and a rear bracket 115. Theshaft of the rotor 1 is rotatably supported by bearings 102F and 102Rmounted on the front and rear brackets 114 and 115, respectively. Theslip rings 109 are in contact with brushes 108 so as to feed power tothe field winding 112 for creating rotor magnetic poles. The statorwinding consists of three-phase coil groups as described with theforegoing embodiments. The coil ends of the respective coil groups areconnected to a rectifying circuit 111. The rectifying circuit 111comprises rectifying elements such as diodes and is wired in full-waverectifier configuration. In the case where diodes are used as rectifyingelements, their cathode terminals are connected to a terminal 106 whiletheir anode terminals are electrically connected to the casing of thein-vehicle alternator 100. A rear cover 110 serves as a protectivecasing for the rectifying circuit 111.

Now, the operation of generating power will be described. An engine (notshown) is mechanically coupled to the in-vehicle alternator 100 via abelt. The in-vehicle alternator 100 is coupled to the engine via thepulley 101 and the belt, and when the engine revolves, the rotor 1 alsorevolves. By passing current through the field winding 112 provided inthe central portion of the nail-shaped magnetic poles 113 of the rotor1, the nail-shaped magnetic poles 113 are magnetized so that therevolution of the rotor 1 causes three-phase voltages to be inducedacross the stator windings. These voltages are full-wave rectified bythe rectifying circuit 111 to output a DC voltage. The positive side ofthis DC voltage is connected with the terminal 106 and further with abattery (not shown). The exciting current through the field winding isso controlled as to make the amplitude of the DC voltage fit forcharging the battery though the details of the control mechanism isomitted here.

FIGS. 26A and 26B show examples of three-phase rectifier circuits forthe three-phase windings on the alternator shown in FIG. 25. FIG. 26Acorresponds to the three-phase rectifying circuit adapted to theembodiments shown in FIGS. 1˜9 while FIG. 26B corresponds to thethree-phase rectifying circuit adapted to the embodiments shown in FIG.10 and the flowing figures. The windings for the respective phases areconfigured in three-phase star (or Y) connection. As shown in FIG. 26A,the non-neutral terminals of the star-connected three-phase windings areconnected with six diodes D1+˜D3−. The cathodes of the positive sidediodes D1+˜D3+ are connected in common with the positive terminal of thebattery. The anodes of the negative side diodes Dl−˜D3− are connected incommon with the negative terminal of the battery.

In the rectifying circuit shown in FIG. 26B, the U1 winding of thethree-phase system Y1 is electrically independent from the U2 winding ofthe three-phase system Y2, and the U1 and U2 windings develop acrossthem the voltages whose amplitudes are equal to each other but whosephases are shifted by 30 electrical degrees from each other.Accordingly, the higher portions of both the voltages are selected as aresult of rectification so that the rectified DC current includesripples whose half period is 30 electrical degrees.

In this embodiment, the star-connected windings are employed. However,the delta-connected windings may also be employed. With thedelta-connected windings, the induced voltages can be increased by 11.5%as compared with the voltages induced in the star-connected windings.

Some of the above described embodiments relate to an electric rotatingmachine comprising a stator consisting of stator coil groups throughwhich three-phase currents in a single three-phase system flow, statorteeth around which the stator coil units are wound, and core packs viawhich magnetic flux flowing through the stator teeth is circulated; anda rotor having magnetic poles disposed opposite to the stator teeth,wherein only U- and V-phase coil units, only V- and W-phase coil units,or only W- and U-phase coil units are wound around a particular statortooth.

Others of the above described embodiments relate to an electric rotatingmachine comprising a stator consisting of stator coil groups throughwhich three-phase currents in a single three-phase system flow, statorteeth around which the stator coil units are wound, and core packs viawhich magnetic flux flowing through the stator teeth is circulated; anda stator having magnetic poles disposed opposite to the stator teeth,wherein the normally wound coil units in concentrated windingconfiguration for the U-, V- and W-phase coil groups are inserted in theradially outer portions of the stator slots; the reversely wound coilunits in concentrated winding configuration for the U-, V- and W-phasecoil groups are inserted in the radially inner portions of the statorslots; and the coil groups of each phase are connected in series withone another.

The rest of the above described embodiments relate to an electricrotating machine comprising two three-phase systems, each system havingthe U-, V- and W-phase coil groups, wherein the phase difference inelectrical angle between the two three-phase systems is made roughlyequal to 30 degrees or falls within a range of 20˜40 electrical degrees.

FIGS. 28A and 28B schematically show the two different aspects of aninth embodiment of an electric motor, with its air gap portiondeveloped linearly, illustrating how coils are wound around the statorteeth. FIG. 28A is a view as seen in the direction along the rotaryshaft of the rotor and FIG. 28B is a view as seen in the radialdirection from rotor to the stator. Except the items described below,this embodiment is similar to the preceding embodiments. As shown inFIG. 28A, the electric motor mainly comprises a rotor 1 and a stator 2.The rotor 1 is provided with plural rotor magnetic poles 11, and thestator 2 is provided with plural stator teeth 21 to form stator magneticpoles. Each of the coil units of the three-phase coil groups spansplural teeth 21. Although only the coil units 31 of the U-phase coilgroup are shown in FIGS. 28A and 28B, it should be understood that thelayout of the coil units is such that both the V-phase coil units andthe W-phase coil units are staggered in lagging phase from the U-phasecoil units by 120 electrical degrees along the circumferential directionof rotor. Since the stator teeth 21 are disposed at a regular intervalof 30 electrical degrees, the V-phase coil units and the W-phase coilunits are staggered behind from the U-phase coil units by a distance offour teeth. It is defined here that the V-phase coil units are the coilunits through which flows an alternating current whose phases lag by 120degrees (or leads by 240 degrees) from the alternating current flowingthrough the U-phase coil units, and that the W-phase coil units are thecoil units through which flows an alternating currents whose phases lagby 240 degrees (or leads by 120 degrees) from the alternating currentflowing through the U-phase coil units.

It is noted here that solid line indicates coil units of normal winding(in which the coil conductor is wound around teeth clockwise as viewedradially from the rotor toward the stator), whereas broken line denotescoil units of reverse winding (in which the coil conductor is woundaround teeth counterclockwise as viewed radially from the rotor towardthe stator). As shown in FIGS. 28A and 28B, the coil units of normalwinding are placed in the slots of the stator 2 remotely from the rotor1, but they may be placed closer to the rotor 1 in the slots. As shownin FIGS. 28A and 28B, two U-phase coil units of concentrated winding,each having two turns and wound in the normal direction, are staggeredfrom each other by 180 electrical degrees, and connected in series witheach other. Another similar U-phase coil units of concentrated winding,having two turns but wound in the reverse direction, are disposedbetween the adjacent normally wound coil units separated by 180electrical degrees from each other. The teeth of the stator 2 aredisposed opposite to the magnetic poles of the rotor 1, with an air gapbetween them. Each normally wound coil unit spans six teeth 21 ingeneral, to form a stator magnetic pole 91 while each reversely woundcoil unit spans six teeth 21 in general, to form another stator magneticpole 92. In each of such coil units, one of the two turns spans sixteeth in full (i.e. 180 electrical degrees) while the other turn spansless teeth (i.e. less than 180 electrical degrees). To be concrete, theother turn spans four teeth 21. If each coil unit has more than twoturns, more than one turn may span four teeth. In the electric motoraccording to this embodiment, the coil conductors are so wound that thecoil turns forming the stator magnetic pole 91 may not overlap the coilturns forming the stator magnetic pole 92 and that the stator magneticpoles 91 and 92 may exhibit opposite magnetic polarities with respect toeach other.

Here, the coil turns (or coil units) forming the two stator magneticpoles 91 and 92 are staggered by 180 electrical degrees from each other.The repetition of the layout of these coil units constitutes each of theU-, V- and W-phase coil groups, these three-phase coil groups beingstaggered by 60 electrical degrees from one another. The V- and W-phasecoil groups are not shown in FIGS. 28A and 28B. Each coil unit of theV-phase coil group is staggered by two teeth from and wound in thereverse direction with respect to, each coil unit of the U-phase coilgroup. Since +60 degrees−180 degrees=−120 degrees, the V-phase coilgroup lags in phase behind the U-phase coil group by 120 electricaldegrees. Since each coil unit of the W-phase coil group is staggered byfour teeth from and wound in the same direction with respect to, eachcoil unit of the U-phase coil group, the W-phase coil group leads inphase the U-phase coil group by 120 electrical degrees (i.e. 2×60electrical degrees).

As compared with the conventional concentrated winding structure where asingle concentrated winding is provided within a range of 360 electricaldegrees, the area of the coil turn circuit cutting the magnetic fluxgenerated by the rotor, according to the stator winding structure ofthis embodiment, is doubled so that the coil utility factor is alsodoubled. In order to obtain the same flux linkage, the number of coilturns around, for example, a particular stator magnetic pole can behalved as compared with the number of corresponding coil turns in theconventional concentrated winding structure. The coil units of the U-,V- and W-phase coil groups are dispersed over the range of electricalangles that is twice as wide as that for the conventional concentratedwinding structure. Moreover, according to this embodiment, differentfrom the way of winding coil conductor in the conventional concentratedwinding structure where all the turns of any coil unit are wound aroundthe same number of teeth, all but one of the plural turns of any coilunit are wound around ⅔ of the entire teeth forming one stator magneticpole while the one remaining turn is wound around the rest (⅓) of theentire teeth. This winding structure can reduce the overall coilinductance as compared with the conventional concentrated or distributedwinding structure.

The coil units of the U-, V- and W-phase coil groups are dispersed overthe range of electrical angles that is twice as wide as that for theconventional concentrated winding structure, and also overlap oneanother by about half of coil span. Accordingly, the armature reactionis relatively smoothly distributed along circumferential direction ascompared with the conventional concentrated winding structure, so thatthe higher harmonic components of electromagnetic force can be reduced.Thus, electric motord using this embodiment will operate with lessoperating noise as compared with electric motors using the conventionalconcentrated winding structure.

In the embodiment shown in FIGS. 28A and 28B, the stator teeth areseparated from one another by 30 electrical degrees and the multipleturns of each coil unit span four stator teeth. The same effect,however, can be obtained if the multiple turns span two, three or fivestator teeth.

Another embodiment will be described next. In the embodiment shown inFIGS. 28A and 28B, an even number of coil turns are wound around statorteeth within the range of 360 electrical degrees, but an odd number ofcoil turns are wound around stator teeth within the range of 360electrical degrees in this embodiment shown in FIGS. 29A and 29B. Exceptthe items described below, this embodiment is similar to the previousembodiment. The stator coils in this embodiment are differently wound ascompared with those in the embodiment shown in FIGS. 28A and 28B. In theembodiment shown in FIGS. 28A and 28B, for each phase, normally woundcoil units and reversely wound coil units are alternately disposed inthe circumferential direction; the normally wound coil units areconnected in series with one another to form a normally wound coil groupwhile the reversely wound coil units are connected in series with oneanother to form a reversely wound coil group; and the normally woundcoil group and the reversely wound coil group are connected in serieswith each other at their coil ends. In this embodiment, however, foreach phase, normally wound coil units and reversely wound coil units arealternately disposed in the circumferential direction and these coilunits are connected in series with one another to form a so-calledalternately flipped-wound coil group. In the embodiment shown in FIGS.28A and 28B, since the normally wound coil units are connected in serieswith one another while the reversely wound coil units are connected inseries with one another, useless coil end portions appear at an intervalof 180 electrical degrees. On the other hand, in this embodiment,normally wound coil units and reversely wound coil units are connectedalternately in series with one another so that no useless coil endportions are formed, with the result that coil utility factor is greaterin this embodiment than in the first embodiment of this invention.

The winding structure in which the respective phase coil groups areevenly distributed in the stator slots in the radial direction, is verypreferable in configuring a uniform three-phase AC system.

FIGS. 30A and 30B schematically show in two different aspects aneleventh embodiment of an electric motor and FIGS. 31A and 31Bschematically show in two different aspects a twelfth embodiment of anelectric motor, illustrating how coils are wound around the stator teethso that the U-, V- and W-phase coil groups may be electrically uniformlydistributed in the stator core along the circumferential direction.Since one coil side of each coil turn is inserted in the deeper positionin a slot than the other coil side of the same coil turn, thedistribution in the radial direction of the coil conductors of therespective phase coil groups becomes uniform so that the coil inductancedistributed along the circumferential direction also becomes uniform.

The last four embodiments described above relate to a single three-phasesystem, but twin three-phase system having two systems of coil groupsstaggered in phase by about 30 degrees from each other will bepreferably employed in order to reduce mechanical noise due to thehigher harmonic components of electromagnetic force. The phase shift θis such that 20 degrees<θ<30 degrees. The twin system consist of a firstthree-phase coil groups of U-, V- and W-phases and a second three-phasecoil groups of U′-, V′- and W′-phases. The U′-phase coil group lags inphase the U-phase coil group by θ electrical degrees, the V′-phase coilgroup lags in phase the V-phase coil group by θ electrical degrees, andthe W′-phase coil group lags in phase the W-phase coil group by θelectrical degrees. To be concrete, with the aid of the embodimentsshown in FIGS. 28A through 31B, let the stator coil unit indicated atreference numeral 31 in FIGS. 28A through 31B be assumed to be theU-phase coil unit. Then, the U′-phase coil unit, similarly wound, isshifter to the right of the U-phase coil unit by one stator tooth; theV-phase coil unit, similarly wound, is shifted to the right of theU′-phase coil unit by three teeth; the V′-phase coil unit, similarlywound, is shifted to the right of the V-phase coil unit by one tooth;the W-phase coil unit, similarly wound, is shifted to the right of theV′-phase coil unit by three teeth; and the W′-phase coil unit, similarlywound, is shifted to the right of the W-phase coil unit by one tooth. Asa result, twin three-phase coil system is completed.

One of the above described embodiments provides an electric motorcomprising a rotor having plural magnetic poles along its periphery anda stator whose teeth are disposed opposite to the periphery of therotor, wherein the coil conductors are wound on the stator so that twostator magnetic poles may be formed by two coil units of a phase woundaround stator teeth within a range of 360 electrical degrees subtendedby the magnetic poles of the rotor; each of the two coil units formingthe stator magnetic poles spans an electrical angle equal to or lessthan 180 electrical degrees; each coil unit has multiple turns within arange narrower than 180 electrical degrees; the coil turns of the twocoil units forming the two stator magnetic poles are laid out such thatthey may not overlap each other; and the coil conductors are so woundthat the adjacent stator magnetic poles exhibit opposite magneticpolarities.

Another embodiment preferably provides an electric motor wherein twocoil units forming two adjacent stator magnetic poles are staggered by180 electrical degrees from each other.

Another embodiment preferably provides an electric motor wherein thestator winding consists of three-phase coil groups forming three-phasemagnetic poles, one phase coil group being staggered by 120 electricaldegrees from another.

Another embodiment preferably provides an electric motor wherein eachcoil unit of each phase coil group, having plural turns, inserted in thestator slots spans 90, 120 or 150 electrical degrees in thecircumferential direction.

Another embodiment preferably provides an electric motor wherein onecoil side of each coil unit is inserted in a slot remotely from therotor while the other coil side of the same coil unit is inserted inanother slot, close to the rotor.

Another embodiment preferably provides an electric motor wherein thecoil conductors are so wound on the stator that two magnetic poles of aphase, formed by two coil units of the same phase, each having two ortwo and a half turns, are disposed within a range of 360 electricaldegrees subtended by the magnetic poles of the rotor.

Another embodiment preferably provides an electric motor wherein thecoil conductor is wound such that each of the coil units of each phasecoil group spans 180 electrical degrees to form a stator magnetic polefor one of the three-phases; after being wound around the teeth formingthe stator magnetic pole of a phase, the coil conductor then leaves theslot where it was last inserted; and after leaving the last insertedslot, the coil conductor is then inserted in a slot that is distanced by180 electrical degrees from the last inserted slot, and starts beingwound in the opposite direction with respect to the direction of windingthe coil conductor around the above mentioned stator magnetic pole, toform another stator magnetic pole of the same phase.

Another embodiment preferably provides an electric motor wherein thecoil conductor is wound such that each of the coil units of each phasecoil group has its number of turns equal to an integer plus half unity,and spans 180 electrical degrees to form a stator magnetic pole for oneof the three phases; after being wound around the teeth forming thestator magnetic pole, the coil conductor then leaves the slot where itwas last inserted; and after leaving the last inserted slot, the coilconductor is inserted in a slot that is distanced by 180 electricaldegrees from the last inserted slot, and starts being reversely woundaround the teeth to form another stator magnetic pole of the same phase.

Another embodiment preferably provides an electric motor wherein thecoil conductor is so wound that a normally wound coil unit spans 180electrical degrees in the circumferential direction to form a normallywound stator magnetic pole; the coil conductor of the normally woundcoil unit leaves the last inserted slot; the coil conductor, afterleaving the last inserted slot, enters a slot distanced by 180electrical degrees from the last inserted slot; and another normallywound coil unit is formed by winding the coil conductor in the samedirection as around the normally wound stator magnetic pole, to formanother normally wound stator magnetic pole, and wherein the coilconductor is so wound that a reversely wound coil unit spans 180electrical degrees in the circumferential direction to form a reverselywound stator magnetic pole within the region of 180 electrical degreesbetween the above described two normally wound coil units, so that thephase of the current through the coil unit wound around the reverselywound stator magnetic pole is shifted by 180 degrees from the phase ofthe current through the coil unit wound around the normally wound statormagnetic pole; the coil conductor of the reversely wound coil unitleaves the last inserted slot; the coil conductor, after leaving thelast inserted slot, enters a slot distanced by 180 electrical degreesfrom the last inserted slot; and another reversely wound coil unit isformed by winding the coil conductor in the same direction as around thereversely wound stator magnetic pole to form another reversely woundstator magnetic pole.

Another embodiment preferably provides an electric motor wherein a thirdcoil group different from the normally wound coil unit and the reverselywound coil unit, is added to the coil structure as described just above;the added coil group is in the wave winding, and each coil unit of thewave winding spans 180 electrical degrees so that the coil conductorpasses through one of the slots in which the normally wound coil unit isinserted and one of the slots in which the reversely wound coil unit isinserted.

Another embodiment preferably provides an electric motor wherein thecoil conductor is so wound that a normally wound coil unit in the wavewinding configuration spans 180 electrical degrees in thecircumferential direction to form a normally wound stator magnetic pole;the coil conductor of the normally wound coil unit leaves the lastinserted slot; the coil conductor, after leaving the last inserted slot,enters a slot distanced by 180 electrical degrees from the last insertedslot; and another normally wound coil unit is formed by winding the coilconductor in the wave winding configuration in the same direction asaround the normally wound stator magnetic pole, to form another normallywound stator magnetic pole, and wherein the coil conductor is so woundthat a reversely wound coil unit in the wave winding configuration spans180 electrical degrees in the circumferential direction to form areversely wound stator magnetic pole within the region of 180 electricaldegrees between the above described two normally wound coil units, sothat the phase of the current through the coil unit wound around thereversely wound stator magnetic pole is shifted by 180 degrees from thephase of the current through the coil unit wound around the normallywound stator magnetic pole; the coil conductor of the reversely woundcoil unit leaves the last inserted slot; the coil conductor, afterleaving the last inserted slot, enters a slot distanced by 180electrical degrees from the last inserted slot; and another reverselywound coil unit is formed by winding the coil conductor in the wavewinding configuration in the same direction as around the reverselywound stator magnetic pole to form another reversely wound statormagnetic pole.

Another embodiment preferably provides an electric motor comprising arotor having plural magnetic poles in the circumferential direction anda stator having a first group of windings and a second group of windingsof the same configuration as the first group of windings, wherein thephase difference in electrical angle between the two groups of windingsfalls within a range of 20˜40 electrical degrees.

Another embodiment preferably provides an electric motor as describedjust above, wherein each of the two groups of windings constitutesmagnetic poles for three-phase system; the coil unit of the firstwinding group and the coil unit of the second winding group, whosephases differ by 20˜40 electrical degrees from each other, span adjacentteeth; and one coil side of each coil unit is inserted in a slotremotely from the rotor while the other coil side of the same coil unitis inserted in another slot closely to the rotor, so that the coil endportions of the two coil units may not overlap each other.

Another embodiment preferably provides an electric motor wherein thestator core has twelve slots within the range of 360 electrical degrees;and each coil unit spans 90, 120 or 150 electrical degrees in thecircumferential direction.

Another embodiment preferably provides an electric motor comprising arotor and a stator, wherein the rotor has plural magnetic poles in thecircumferential direction; the stator has a first group of windings anda second group of windings different in configuration from the firstgroup of windings; the phase difference in electrical angle between thetwo groups of windings falls within a range of 20˜40 electrical degrees;and the numbers of the coil elements inserted in the individual slotsare the same.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An electric motor, comprising: a rotor having plural magnetic polesalong its periphery; and a stator having teeth that are disposedopposite to the periphery of the rotor; wherein, the stator includes twostator magnetic poles of the same phase, each of which is formed by atooth, a first coil turn, and a second coil turn coupled in series withthe first coil turn and having a polarity opposite to a polarity of thefirst coil turn, within a range of 360 electrical degrees subtended bythe magnetic poles of the rotor; each of the first coil turn and thesecond coil turn is wound so as to span an electrical angle less than180 electrical degrees in a circumferential direction; and a toothconstituting a part of a stator magnetic pole of the other phase isdisposed between the first coil turn and the second coil turn.
 2. Anelectric motor as claimed in claim 1, wherein the first coil turn andthe second coil turn are staggered by 180 electrical degrees from eachother.
 3. An electric motor as claimed in claim 1, wherein the statorwinding comprises three-phase coil groups forming three-phase magneticpoles, the three-phase coil groups being staggered by 120 electricaldegrees from one another.
 4. An electric motor as claimed in claim 1,wherein each of the first coil turn and the second coil turn spans oneof 90, 120 and 150 electrical degrees in the circumferential direction.5. An electric motor as claimed in claim 1, wherein one of the firstcoil turn and the second coil turn is disposed in a slot remote from therotor, while the other of the first coil turn and the second coil turnis disposed in another slot, close to the rotor.
 6. An electric motor asclaimed in claim 1, wherein the coil conductors are so wound on thestator that two magnetic poles of a phase, formed by the tooth, eachhaving two or two and a half turns, are disposed within a range of 360electrical degrees subtended by the magnetic poles of the rotor.
 7. Anelectric motor as claimed in claim 1, wherein: each of the coil turns ofeach phase coil group spans 120 electrical degrees in thecircumferential direction, to form a stator magnetic pole for one of thethree-phases; after winding around the teeth forming the stator magneticpole of a phase, the coil conductor leaves the slot where it was lastinserted; and after leaving the last inserted slot, the coil conductoris then inserted in a slot that is distanced by 180 electrical degreesfrom the last inserted slot, and starts being wound in the oppositedirection with respect to the direction of winding the first coil turnaround the above mentioned stator magnetic pole, to form another statormagnetic pole of the same phase.
 8. An electric motor as claimed inclaim 1, wherein: each of the coil conductors of each phase coil grouphas its number of turns equal to an integer plus half unity, and spans120 electrical degrees to form a stator magnetic pole for one of thethree phases; after winding the teeth forming the stator magnetic pole,the coil conductor then leaves the slot where it was last inserted; andafter leaving the last inserted slot, the coil conductor is inserted ina slot that is distanced by 180 electrical degrees from the lastinserted slot, and starts winding in the opposite direction with respectto the direction of winding the first coil turn around the abovementioned stator magnetic pole, to form another stator magnetic pole ofthe same phase.
 9. An electric motor as claimed in claim 1, wherein: thecoil conductor is so wound that a normally wound coil conductor spans120 electrical degrees in the circumferential direction to form anormally wound stator magnetic pole; the coil conductor of the normallywound coil conductor leaves the last inserted slot; the coil conductor,after leaving the last inserted slot, enters a slot distanced by 240electrical degrees from the last inserted slot; another normally woundcoil conductor is formed by winding the first coil turn in the samedirection as around the normally wound stator magnetic pole, to formanother normally wound stator magnetic pole; the coil conductor is sowound that a reversely wound coil conductor spans 120 electrical degreesin the circumferential direction to form a reversely wound statormagnetic pole within a region of 240 electrical degrees between theabove described two normally wound coil conductors, so that the phase ofthe current through the coil conductor wound around the reversely woundstator magnetic pole is shifted by 180 degrees from the phase of thecurrent through the coil conductor wound around the normally woundstator magnetic pole; the coil conductor of the reversely wound coilconductor leaves the last inserted slot; after leaving the last insertedslot, the coil conductor enters a slot distanced by 180 electricaldegrees from the last inserted slot; and another reversely wound coilconductor is formed by winding the second coil turn in the samedirection as around the above mentioned reversely wound stator magneticpole to form another reversely wound stator magnetic pole.
 10. Anelectric motor as claimed in claim 9, wherein: a third coil groupdifferent from the normally wound coil conductors and the reverselywound coil conductors, is added to the coil structure; the added coilgroup is in a wave winding; and each coil conductor of the wave windingspans 180 electrical degrees so that the coil conductor passes throughone of the two slots in which the first coil turn and the second coilturn are reversely inserted.
 11. An electric motor as claimed in claim1, wherein: the coil conductor is so wound that a normally wound coilconductor in a wave winding configuration spans 120 electrical degreesin the circumferential direction to form a normally wound statormagnetic pole; the coil conductor of the normally wound coil conductorleaves the last inserted slot; after leaving the last inserted slot, thecoil conductor enters a slot distanced by 240 electrical degrees fromthe last inserted slot; another normally wound coil conductor is formedby winding the coil conductor in the wave winding configuration in thesame direction as the first coil turn around the normally wound statormagnetic pole, to form another normally wound stator magnetic pole; thecoil conductor is so wound that a reversely wound coil conductor in thewave winding configuration spans 120 electrical degrees in thecircumferential direction to form a reversely wound stator magnetic polewithin the region of 240 electrical degrees between the above describedtwo normally wound coil conductors, so that a phase of current throughthe coil conductor wound around the reversely wound stator magnetic poleis shifted by 180 degrees from a phase of current through the coilconductor wound around the normally wound stator magnetic pole; the coilconductor of the reversely wound coil conductor leaves the last insertedslot; after leaving the last inserted slot, the coil conductor enters aslot distanced by 240 electrical degrees from the last inserted slot;and another reversely wound coil conductor is wound in the wave windingconfiguration in the same direction as the second coil turn around thereversely wound stator magnetic pole, to form another reversely woundstator magnetic pole.
 12. An electric motor as claimed in claim 1,wherein the first coil turn and the second coil turn do not overlap eachother.
 13. An electric motor as claimed in claim 1, wherein: each of thecoil conductors of each phase coil group is wound so as to span 150electrical degrees to form a stator magnetic pole for one of the threephases; after winding around the teeth forming the stator magnetic pole,the coil conductor leaves the slot where it was last inserted; and afterleaving the last inserted slot, the coil conductor is inserted in a slotthat is distanced by 180 electrical degrees from the last inserted slot,and starts winding in the opposite direction relative to the directionof winding the first coil turn around the above mentioned statormagnetic pole, to form another stator magnetic pole of the same phase.14. An electric motor as claimed in claim 1, wherein: each of the coilconductors of each phase coil group has a number of turns equal to aninteger plus half unity, and spans 150 electrical degrees to form astator magnetic pole for one of the three phases; after winding aroundthe teeth forming the stator magnetic pole, the coil conductor leavesthe slot where it was last inserted; and after leaving the last insertedslot, the coil conductor is inserted in a slot that is distanced by 180electrical degrees from the last inserted slot, and starts winding inthe opposite direction with respect to the direction of winding thefirst coil turn around the above mentioned stator magnetic pole, to formanother stator magnetic pole of the same phase.
 15. An electric motor asclaimed in claim 1, wherein: the coil conductor is so wound that anormally wound coil conductor spans 150 electrical degrees in thecircumferential direction to form a normally wound stator magnetic pole;the coil conductor of the normally wound coil conductor leaves the lastinserted slot; after leaving the last inserted slot, the coil conductorenters a slot distanced by 240 electrical degrees from the last insertedslot; another normally wound coil conductor is formed by winding thecoil conductor in the same direction as the first coil turn around thenormally wound stator magnetic pole, to form another normally woundstator magnetic pole; the coil conductor is so wound that a reverselywound coil conductor spans 150 electrical degrees in the circumferentialdirection to form a reversely wound stator magnetic pole within theregion of 240 electrical degrees between the above described twonormally wound coil conductors, so that a phase of current through thecoil conductor wound around the reversely wound stator magnetic pole isshifted by 150 degrees from a phase of current through the coilconductor wound around the normally wound stator magnetic pole; the coilconductor of the reversely wound coil conductor leaves the last insertedslot; after leaving the last inserted slot, the coil conductor enters aslot distanced by 240 electrical degrees from the last inserted slot;and another reversely wound coil conductor is formed by winding the coilconductor in the same direction as the second coil turn around thereversely wound stator magnetic pole to form another reversely woundstator magnetic pole.
 16. An electric motor as claimed in claim 15,wherein: a third coil group, different from the normally wound coilconductors and the reversely wound coil conductors, is added to the coilstructure; the added coil group is in the wave winding; and each coilconductor of the wave winding spans 180 electrical degrees so that thecoil conductor passes through one of the two slots in which the firstcoil turn and the second coil turn are reversely inserted.
 17. Anelectric motor as claimed in claim 1, wherein: the coil conductor is sowound that a normally wound coil conductor in the wave windingconfiguration spans 150 electrical degrees in the circumferentialdirection to form a normally wound stator magnetic pole; the coilconductor of the normally wound coil conductor leaves the last insertedslot; after leaving the last inserted slot, the coil conductor enters aslot distanced by 240 electrical degrees from the last inserted slot;another normally wound coil conductor is wound in the wave windingconfiguration in the same direction as the first coil turn around thenormally wound stator magnetic pole, to form another normally woundstator magnetic pole; the coil conductor is so wound that a reverselywound coil conductor in the wave winding configuration spans 150electrical degrees in the circumferential direction to form a reverselywound stator magnetic pole within the region of 240 electrical degreesbetween the above described two normally wound coil conductors, so thatthe phase of the current through the coil conductor wound around thereversely wound stator magnetic pole is shifted by 180 degrees from thephase of the current through the coil conductor wound around thenormally wound stator magnetic pole; the coil conductor of the reverselywound coil conductor leaves a last inserted slot; after leaving the lastinserted slot, the coil conductor enters a slot distanced by 240electrical degrees from the last inserted slot; and another reverselywound coil conductor is formed by winding the coil conductor in the wavewinding configuration in the same direction as the second coil turnaround the reversely wound stator magnetic pole to form anotherreversely wound stator magnetic pole.